The present invention relates generally to solar heat collection panels. More particularly, the invention relates to thin film solar collectors.
Solar heat collection panels have been used for a number of years to heat or preheat water and/or other fluids for a number of applications. Many collectors utilize a metal collection plate having a number of metal riser tubes or tubes with fins that extend between header pipes (often called manifolds). Often, the collection plates are housed within an insulated box with a transparent glazing placed over the front surface of the collector panel.
Another type of solar heat collection panel contemplates eliminating the collection plate and rather simply runs a series of side-by-side riser tubes between a pair of header pipes. The header pipes and risers can be formed from a wide variety of materials, but one class of heat exchangers use simple extruded plastic or elastomer tubing. When plastic tubing is used as the risers, adjacent tubes can be extruded, tack welded or supported together so that an array of side-by-side tubes forms a collection panel. A variety of plastics may be used to form the panels, although generally a dark, thermoplastic material is used. Such panels have been sold for a number of years by FAFCO Inc. of Chico, Calif., and are described, for example, in U.S. Pat. No. 4,205,662.
Although these and other existing solar panel designs work quite well, there are continuing efforts to develop new collector designs that meet the needs of specific applications and/or to further decrease costs.
U.S. Pat. No. 4,143,644 describes a solar panel design that is formed by welding two plastic sheets together. Although the patent describes a low cost collector design, the design does not appear to have enjoyed substantial commercial success. It is believe that one of the reasons for this is that the described design appears to be highly susceptible to: (a) stress concentrations that can lead to collector failures due to delamination of the welded sheets; and (b) kinking or other deformation of the flow paths, which can significantly reduce the efficacy of the collector. Furthermore, the '644 patent contemplates the use of just one fluid supply line and one fluid return line for communicating between its fluid reservoir and the collector flow channels which accentuates the risk of flow interruptions due to kinking or the like. These risks are even further accentuated by the fact that the only lines in communication with the reservoir are located on peripheral sides of the collector near tie down structures (i.e. holes 8) used to hold the collector in place.